The research program is designed to provide information on basic aspects of neutron capture therapy. This information will provide the basis for application of NCT in therapy of many diseases. The first portion of the study deals with the optimal design of an epithermal neutron source suitable for use in a hospital environment. The availability of epithermal neutrons will permit NCT to be employed in brain and in other organs without surgery. Fractionated therapy may be possible. Track etch autoradiography will be used to determine the distribution of compounds on a cellular basis in biological tissue. The technique will be used with scanning and transmission electron microscopy to determine radiobiological response. Track etch autoradiography will also be employed to determine the biodistribution of boron labelled compounds on a macroscopic basis. The possible use of positron emission tomography to quantitate concentrations of boron compounds in tissues will be investigated.